Land mobile radio (LMR) networks are critical for public safety communications. In general LMR systems are embodied within conventional, trunked or a combination of conventional and trunked systems. Two-way radios, also referred to as subscriber units, operating within the LMR system can transmit as well as receive and provide users with the ability to wirelessly communicate over a radio channel. Two-way radios are available in mobile, stationary base, hand-held portable, and vehicle mounted configurations.
Scanning techniques are used in two-way radio communication systems to monitor call activity amongst a group of radios or across multiples groups of radios. Members of the group or groups are typically referred to as scan list members. From a user standpoint, scanning allows a radio user involved in a group call or individual call to simultaneously scan for any call activity occurring amongst the scan list members and join a call already in-progress. Thus, a radio user, such as a supervisor, can effectively monitor a number of different groups and take part in their calls as required. When scanning, a radio spends time checking for activity from every member in the scan list regardless of whether or not the subscriber is in the coverage area of a given list member. Scanning for activity from every member takes a considerable amount of time. Current scan list implementations limit the number of channels that can be in the list in order to limit the total time it takes to check for activity on any one of the channels. For this reason, it is impractical to have large scan lists or merge a multi-frequency scan system with other conventional channels into one list since the likelihood of missed activity increases.
Accordingly, there is a need for an improved scanning technique to be used within a two-way radio communication system.
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